The present exemplary embodiment relates to energy scavengers. It finds particular application in conjunction with cantilevered vibrational energy scavengers, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
In designing vibrational energy harvesters, a system must be able to adjust its resonant or natural frequency. This is required so that the resonant frequency of the system is the same as the most energetic, excitation frequency. When this is matched, the energy harvested is optimized. This can be seen in the equation below (from Roundy), which describes the power which may be harvested by a piezo bimorph beam, as a function of mass M, electrical damping E, beam natural frequency Wn, excitation frequency W, beam displacement Y, and total damping ζT. The power is maximized when the ratio of excitation to natural frequency approaches 1.
          P        =            m      ⁢                          ⁢              ξ        e            ⁢              ω        n            ⁢                                    ω            2                    ⁡                      (                          ω                              ω                n                                      )                          2            ⁢              Y        2                                      (                      2            ⁢                          ζ              T                        ⁢                          ω                              ω                n                                              )                2            +                        (                      1            -                                          (                                  ω                                      ω                    n                                                  )                            2                                )                2            
Although apparently feasible at a theoretical level, a need exists for a device and method for optimally harvesting vibrational energy.